Effetti delle sostanze umiche sull'assorbimento dell'azoto in mais (Zea mays L.)

The thriving interest in lignosulfonates (LSs) as agricultural biostimulants necessitates a comprehensive understanding of their chemistry and resultant effects on plant physiology. This study investigates the efficacy of four distinct LSs (A, B, C, and D) with two dosages (2 mg l-1 and 4 mg l-1) in enhancing the performance of maize (Zea mays L.) under hydroponic conditions. Maize seedlings were exposed for six days to different concentrations of these products added to the nutrient solution, and their impact on growth, biomass, and nitrogen metabolism was assessed. Root length exhibited a substantial increase ranging from 12% to 61% compared to the control, and improved leaf biomass was observed. This physiological response to LSs was associated with a modulation in the gene expression profile of key players in nitrate transport and assimilation. The genes analysed are ZmNRT2.1 and ZmNRT2.2 (for low-affinity transport), ZmNRA2.1 (for accessory proteins), ZmMha2 (for H+-ATPase), ZmGOGTA (for glutamate synthase), and ZmNr (for nitrate reductase). The first three are over-expressed in leaves and roots. ZmMha is over-expressed in the leaves of maize seedlings treated for four hours with the lowest dose of product C. ZmGOGTA is over-expressed in the roots of seedlings treated for four hours with the highest dose of product C. ZmNr is over-expressed by C, concentration 4 mg l-1 in the leaves, and by A and C, in the roots. Seedlings treated with products A (4 mg l-1) and C (4 mg l-1) showed the highest nitrate uptake rates of 0.339 and 0.450 µM NO3- per minute, respectively, higher than the control group’s 0.233 µM NO3- min-1. Products B (2 mg l-1) and D (4 mg l-1) also improved uptake to 0.305 and 0.326 µM NO3- min-1, suggesting these treatments could improve the nitrate uptake as compared to the control. In conclusion, the LSs under study demonstrated biostimulant properties. This could be attributed to the raw materials and processing methods employed in their production, which likely influenced their chemical characteristics. The findings illuminate the potential of LSs to enhance nitrogen use efficiency in crops, presenting a promising avenue for sustainable agricultural practices.